With high-speed and high-density signal transmissions between electronic elements or between circuit boards in recent years, an increase in speed and density by transmissions via electrical wiring in the related art is approaching the limit because of an obstacle, such as mutual interference and attenuation of signals. In order to overcome such an obstacle, a technique of connecting one electronic element to another or one circuit board to another by means of light, so-called optical interconnection, is under study. Attention is being given to a polymer optical waveguide because it can be easily processed into an optical transmission path, it is inexpensive, a degree of freedom in wiring is high, and a density can be increased.
For a device using such optical communications, it is necessary to couple a light signal and an electrical signal to each other. Hence, it is necessary to bring optical axes of the optical waveguide and the light receiving and emitting element into agreement with each other. As a method of coupling a light signal and an electrical signal, it is general to use an optical axis conversion mirror configured to totally reflect light on an inclined surface that is preliminarily formed at an end of a core at an angle of 45 degrees with respect to a longitudinal direction of the core.
Incidentally, in order to bring the optical axes into agreement with each other by disposing an optical waveguide substrate and an electric circuit board in lamination, the following is proposed. That is, alignment markers are provided to both of the optical waveguide substrate and the electric circuit board. Hence, by matching these alignment marks, an optical axis of a light receiving and emitting element on the electric circuit board and an optical axis of the optical waveguide in the optical waveguide substrate can be aligned with respect to each other easily in a reliable manner (see Paragraph 0028 in Patent Document 1).
Also, there is proposed an optical element mounted wiring board in which a film-like optical waveguide is disposed on a ceramic substrate, which is a multi-layer wiring board and has a metal wiring layer as an inner layer, by fitting a guide pin into an alignment hole (see Paragraphs 0054 through 0059 in Patent Document 2).
Patent Documents 1 and 2, however, fail to provide detailed descriptions as to in which manner the alignment marker and the alignment hole are obtained with accuracy. Hence, these disclosures are proposals on the precondition that the alignment marker and the alignment hole are formed with a high degree of accuracy.
It is general to adopt the following method as a method of forming the alignment marker and the like. That is, an alignment metal marker is preliminarily formed in the vicinity of an optical waveguide by resist exposure, development, metal deposition, and resist separation processes. Then, an optical axis conversion mirror is manufactured at a constant distance from the marker by a grinding process using a dicer. The optical axes are brought into agreement with each other by this optical axis conversion mirror.